The present invention generally relates to telemetry for implantable medical devices and instruments. Specifically, the invention relates to an arrangement and a method for an implantable medical device (IMD) to distinguish between telemetry downlink signals received from a programming device and noise.
In recent years, implantable medical device (IMD) technology has rapidly advanced. Sizes and weights of these devices have decreased, while functionality has increased. These advances have created a corresponding demand for improved two-way communication or telemetry between the IMD and an external programming device, such as an IMD programmer device. Current telemetry systems are designed to provide two-way telemetry by radio frequency (RF) signal transmission between an antenna coil located within the IMD and an antenna coil located in a programming head of the IMD programmer device. The programming head can be positioned over the patient""s IMD site for programming or telemetry interrogation of the implanted device. Command instructions or data that are downloaded to the IMD are referred to as downlink transmissions, and data transmitted from the IMD to the IMD programmer device are referred to as uplink transmissions.
The IMD programmer device typically communicates with the IMD at a RF frequency of about 175 KHz. The RF carrier signal is modulated with the transmitted data using conventional modulation or encoding schemes that include, but are not limited to, pulse position modulation (PPM), frequency shift keying (FSK), differential binary phase shift keying (DBPSK) and burst counting (active and inactive states). The antenna of the IMD is typically tuned to the 175 KHz center frequency and commences generating output signals when a signal is detected at or near 175 KHz frequency. However, not all signals detected by the IMD antenna are downlink transmissions.
Preserving battery life is a primary consideration in the design of new implanted medical devices. Reducing the number of times that an IMD xe2x80x9cwakes upxe2x80x9d from a power saving sleep mode prevents current drain of the battery. However, the IMD sometimes xe2x80x9cwakes upxe2x80x9d unnecessarily because the IMD erroneously detects what appears to be an interrogation request from the programming device. The IMD at the 175 KHz frequency usually detects a normal interrogation request. Noise may be interpreted by the IMD as an interrogation request because the detected signal is near (above or below) the 175 KHz threshold frequency. After several attempts at processing the incoming signal, the IMD determines that the interrogation request is a false signal, e.g., noise.
Accordingly, there is a need for an arrangement and a method for discriminating between RF signals and noise within an implanted medical device, and that addresses the aforementioned problems, as well as other related problems.
Various embodiments of the present invention are directed to addressing the above and other needs in connection with improving frequency discrimination by a receiving circuit of an implanted medical device. More specifically, the present invention enables the IMD to prolong battery life by reducing the number of times the IMD transitions into a fully operational state after erroneously interpreting noise as a valid communication from an external IMD programmer.
According to one embodiment of the invention, a receiver circuit for an implanted medical device (IMD) discriminates between a radio frequency (RF) signal transmitting data from an external IMD programmer and noise. The IMD includes an antenna that generates output signals in response to telemetry transmissions from the IMD programmer and an analog receiver circuit that amplifies, filters, and compares the output signals to a threshold level to generate a digital signal representative of the RF signal. The receiver circuit further includes a counter circuit that receives the digital signal and counts edges of the digital signal occurring within a selected time period. The receiver circuit also includes a decoder circuit that decodes the counter value and compares the number of edges counted to a predetermined range of values before transmitting the decoded signal to a telemetry processor for further processing. The receiver circuit may also include additional counters that count the edges of the digital signal occurring over different time intervals. Each of these additional counters have an associated decoder circuit to compare the counter value to a predetermined range of values. The receiver circuit also includes an encoding circuit that receives the decoded signals from all of the decoder circuits and generates a plurality of signals for the telemetry processor of the IMD.
According to another embodiment of the invention, a method is provided for discriminating between a radio frequency (RF) signal transmitting data from an external IMD programmer and noise. The IMD includes an antenna that generates output signals in response to telemetry transmissions from the IMD programmer and an analog receiver circuit that amplifies, filters, and compares the output signals to a threshold level to generate a digital signal representative of the RF signal. The method includes counting edges of the digital signal occurring within a selected time period. The method also includes decoding the counter value and comparing the number of edges counted to a predetermined range of values before transmitting the decoded signal to a telemetry processor for further processing. The method may also include counting the edges of the digital signal over different time intervals.
The above summary of the present invention is not intended to describe each illustrated embodiment or every implementation of the present invention. The figures in the detailed description that follow more particularly exemplify these embodiments.